The present invention relates to security devices for memory devices and more specifically to a memory security device and method.
Maintaining control over data within memory devices such as EEPROM's is a problem today. One approach has been to shield chips containing the memory devices from inspection and at the same time erase the memory and prevent operation of the devices upon intrusion.
Commonly assigned U.S. Pat. No. 4,811,288, entitled "Data Security Device for Protecting Stored Data", issued Mar. 7, 1989, to Kleijne et al. discloses a security device for protecting sensitive data stored in a resettable memory, including a housing formed of ceramic plates. A pair of thin film conductive paths are arranged in a meandering configuration on the inner surface of the housing. Interrupting or short circuiting the thin film conductive paths causes reset means to reset the resettable memory thereby erasing the data stored therein.
U.S. Pat. No. 4,933,898 entitled "Secure Integrated Circuit Chip with Conductive Shield", issued Jun. 12, 1990, to Gilberg et al., discloses an integrated circuit chip containing a secure area in which secure data is processed and stored. The chip includes a semiconductor layer containing circuit elements, a first conductive layer coupled to the semiconductor layer to interconnect the circuit elements, and a second conductive layer overlying the circuit elements to define a secure area and coupled to the circuit elements for conducting a predetermined signal which is essential to the intended function of the shielded circuit elements. Removal of the second conductive layer prevents the predetermined signal from being provided to the circuit elements.
While these security devices work well, they may still be defeated by selective etching techniques to defeat the conductive layers. Therefore, it would be desirable to produce a memory security device which cannot be defeated by etching.